The present invention relates to communications systems, and more particularly to mobile satellite communications. Even more particularly, the present invention relates to interference detection in a mobile satellite communications system.
Interference presents a challenging constraint in the operation of satellite systems. Nearby satellites, terrestrial radio transmitters, and microwave sources produce signals that can substantially degrade or disrupt a desired signal in the satellite communications system. These signals may be intentionally designed to interfere with the desired signal, or may be inadvertent. In any case, it is important to quickly detect interference so that the source can be removed, or satellite communications system users moved to other resources.
Traditionally, interference is detected by observing anomalous behavior in the satellite communications system over an extended period of time. By observing anomalous behavior, and by combining these observations with knowledge of possible sources of interference, conclusions are drawn as to the presence of interference. Because, however, traditional methods of detecting interference require observing the communications system over an extended period of time, response to an interference is unacceptably slow. Additionally, using traditional methods, the specific characteristics of the interference are difficult to determine absent a priori knowledge of possible sources of interference, thus making determination of the likely source(s) of the interference more difficult.
The present invention advantageously addresses the needs above as well as other needs by providing a method, and related apparatus, for quickly and precisely detecting an interference in a communication system, in particular in a mobile satellite communication system.
In one embodiment, the invention can be characterized as a method of detecting interference at a first communications terminal comprising establishing a communications link between the first communications terminal and a second communications terminal. Then monitoring a noise floor of the communications link over time, the noise floor representing a base level of noise present in the communications link, and calculating a long term noise floor power level without interference in response to the monitoring of the noise floor of the communications link over time. Then monitoring a noise floor of a current communication through the communications link, this noise floor representing a current level of noise present on the communications link, and calculating a short term noise floor power level in response to the monitoring of the noise floor of the current communication through the communications link, subsequently, comparing the short term noise floor power level with the long term noise floor power level.
In another embodiment, the invention can be characterized as a method of estimating a noise floor power level of a communications link, including receiving a plurality of bursts from the communications link into a communications terminal. Then, generating an error vector magnitude from each of the plurality of bursts and generating a received signal strength indication from each of the plurality of bursts. Then, linearizing the error vector magnitude and the received signal strength indication from each of the plurality of bursts and defining a sample as the difference between the received signal strength indication and the error vector magnitude from each of the plurality of bursts. Finally, averaging a plurality of samples taken over a period of time.
In a further embodiment, the invention can be characterized as a communications system for detecting interference including a first communications terminal for transmitting and receiving signals to and from a second communications terminal and a communications link established between the first communications terminal and the second communications terminal. Also, an interference detector coupled to the first communications terminal, the interference detector including: means for generating a long term noise floor power level of the communications link without interference, means for generating a short term noise floor power level of a current communication using the communications link, and means for comparing the long term noise floor power level and the short term noise floor power level.